Typically, LCDs, which have recently become widely used in the flat display field, suffer because they have a narrow viewing angle. The reasons why an image is differently displayed depending on the viewing angle in LCDs are that, first, there are problems related to the anisotropy of liquid crystals, and, second, a polarizing plate is deficient.
Thus, in order to improve a wide viewing angle of an LCD, a completely dark state and uniform brightness are required. In particular, the VA-LCD, in which the initial orientation of liquid crystals is in the vertical direction, unlike a TN mode, has two problems in regard to deteriorating viewing angle properties, that is, first, the dependence of performance of perpendicular polarizing plates on the viewing angle, and second, the dependence of the birefringence of the VA-LCD panel on the viewing angle.
Various attempts have been made to overcome the obstacles preventing realization of a wide viewing angle of LCDs attributed to such requirements and problems. As specific techniques for improvement, a method of using a viewing angle compensation film for compensating for a narrow viewing angle by changing And (multiplication of birefringence by thickness of a liquid crystal panel) depending on the angle, and a multidomain mode using a pixel, divided into a plurality of domains to improve a viewing angle, have been proposed.
As a specific example for improving the wide viewing angle of the VA-LCD using the viewing angle compensation film, a VA-LCD using a −C-plate compensation film (nx=ny>nz, where nx is the in-plane refractive index in the X-axis direction, ny is the in-plane refractive index in the Y-axis direction, and nz is the refractive index in the Z-axis direction, that is, the thickness direction) for compensating for the dark state of a VA-LCD when voltage is not applied is disclosed in U.S. Pat. No. 4,889,412. However, since the VA-LCD including only the −C-plate compensation film does not completely compensate therefor, light undesirably leaks at tilt angles.
In U.S. Pat. No. 6,141,075, a compensation film comprising a C-plate compensation film and an A-plate compensation film is disclosed, in which compensation for the dark state of the VA-LCD when voltage is not applied is said to be more efficiently realized than in other conventional cases. However, this patent suffers because the minimum contrast ratio at a tilt angle of 70° in a dark state is merely 20:1. Hence, to meet the goal of completely compensating for a viewing angle, contrast at surface-facing angle and tilt angle of LCDs should be improved, and the problem of color shift depending on the viewing angle in a dark state should be solved.